Staircase to a mezzanine

Can anyone give me a rough idea about how much a staircase to a mezzanine might cost? At the moment each tread is sticking out from the wall; no bannisters at all (DH's first job when we get in to the new house is to make each step non-slip, and get a bannister in before I break my neck!)

I'd quite like something contemporary i.e. glass/perspex sides to the staircase, but cost is going to be an issue.